Solar hot water system not working

[Lateron]

Hi,
I hope this is the right forum to post my question.
I have a problem with my solar hot water system. It does not seem to be supplying adequate hot water. Any helpful comments, please!

I have (inherited) an Open solar hot water system (No coils inside tank, the fluid in the collector is potable water and directly connected to the house hot water system) using one vacuum tube panel of 15 tubes, make unknown but I think sourced out of China. The connected tank has 120 l capacity.
The (AC) pump circulating water through the collector to the tank has failed. I have replaced it with a DC pump. For testing purposes I have connected it to a timer which is set to run continuously from 9.00 am to 5 pm each day (I live in Spain where the sun (nearly) always shines).

The system has three temperature sensors; a Pt1000 at the top of the collector (T1), a NTC 10k at the bottom of the tank (T2) and the same kind at the top exit (T3). I took some measurements as follows, with the circulation pump continuously on; ambient day temperature was 31

[LucMan]

What is the delta T temperature ( inlet & outlet).

[Lateron]

For some reason my message was truncated. Here is the last part:

Resistance value of sensor T1 was 1150 Ohm, equating to 40

[Lateron]

Why are my messages truncated???

[NEOH]

Special Symbol (degrees) ??? - not allowed.

[Mike90250]

Quote marks have truncated my messages too

[Lateron]

Solar hot water system not working - retry without special symbols

Hi,
I hope this is the right forum to post my question.
I have a problem with my solar hot water system. It does not seem to be supplying adequate hot water. Any helpful comments, please!

I have (inherited) an Open solar hot water system (No coils inside tank, the fluid in the collector is potable water and directly connected to the house hot water system) using one vacuum tube panel of 15 tubes, make unknown but I think sourced out of China. The connected tank has 120 l capacity.

The (AC) pump circulating water through the collector to the tank has failed. I have replaced it with a DC pump. For testing purposes I have connected it to a timer which is set to run continuously from 9.00 am to 5 pm each day (I live in Spain where the sun (nearly) always shines).

The system has three temperature sensors; a Pt1000 at the top of the collector (T1), a NTC 10k at the bottom of the tank (T2) and the same kind at the top exit (T3). I took some measurements as follows, with the circulation pump continuously on; ambient day temperature was 31 deg.C (88 deg.F):

Resistance value of sensor T1 was 1150 Ohm, equating to 40 deg.C (104 deg.F)
(Laboratory) thermometer temperature measured at T1, under the insulation was 39 deg.C (102 deg.F)
Resistance value of sensor T2 was 4000 Ohm, equating to 47 deg.C (117 deg.F)
Resistance value of sensor T3 was 16000 Ohm, equating to less than 20deg.C (68 deg.F)
Delivered water temperature at exit T3 by thermometer was 40 deg.C

Conclusions:

1. Only 40 deg.C at the collector top seems far too low.
2. Either the T2 sensor is not working properly or the wiring is bad. To be investigated further.
3. Something is really wrong with sensor T3 and / or the wiring. To be investigated further.
4. The collector is working (somewhat) . The DC pump is doing its job. The exit water temperature is the same as the collector water temperature.
5. Sensor T1 is working well.

Question:
What could be the cause of the low circulating water temperature at the top of the collector? (40 deg.C with ambient temperature of 31 deg.C !) Circulation pump continuously on? Collector panel not functioning? (How to test that?).


Anybody have any ideas?

[Mike90250]

Welcome. Thermister sensors are pretty rugged, so if they have not been abused or flooded with water, I suspect they are OK. What about the controller box that is the "brains" of the system ? Any name or model number on it? Getting the manual would be the first thing I would try, if no manual, I'd look to getting a new controller that has instructions. Changing parts and turning knobs at random seldom produces the best results.

[LucMan]

Sounds like you are not absorbing any heat from your tubes. There are several reasons that can happen.
The heat pipes are not making good contact with the inside of the header sockets. They could be loose or have corrosion on the bulb.
The heat pipes froze and lost the heat transfer fluid. Repair may be possible or you may be able to purchase replacements.
The evacuated tubes are defective. Replacement required.
Using an infrared thermometer you can check each EV tube to see if they are hot on the outside.
The heat pipes can be checked by removing the EV tubes and visually checking for splits on the bottom where the fluid would sit. Then remove them from the header with a twisting motion.
There may be several defective tubes so check them all.

[Lateron]

The controller is a Chinese made "SR868C6" and I have the instruction manual. I have disconnected it for now. It too was showing low temperatures when connected and that is when I discovered that the AC pump which it controlled was defective.

I am going to try and check the heat pipes but I wonder if that is a simple as LucMan suggests! Not having an infrared thermometer I am first going to go on feel, checking the feel-temperature (warm, hot, bl..dy hot) of all 15 tubes. I

[Lateron]

Back on the roof to feel the heat pipes. On the outside they are lukewarm. The manifold is hotter, about 40 degC I guess. I can twist a tube but do not know how to remove it from its holder - which is a cap at the bottom end of the tube and fairly inaccessible. (This is a split system with the collector on a sloping roof and the tank some 4 meters away.) The top of the tubes disappear into a cover held down by at least 4 screws on each side, through which the inlet & outlet pipes protrude. I am not sure if unscrewing the ends will let me get at the tubes. Any advice?

[AzRoute66]

Might be a good day to learn how to post pictures. Not for me, I have no clue, but just saying...